78 research outputs found
Quantum state reconstruction via continuous measurement
We present a new procedure for quantum state reconstruction based on weak
continuous measurement of an ensemble average. By applying controlled evolution
to the initial state new information is continually mapped onto the measured
observable. A Bayesian filter is then used to update the state-estimate in
accordance with the measurement record. This generalizes the standard paradigm
for quantum tomography based on strong, destructive measurements on separate
ensembles. This approach to state estimation can be non-destructive and
real-time, giving information about observables whose evolution cannot be
described classically, opening the door to new types of quantum feedback
control.Comment: 4 pages, 2 figure
Quantum Control of the Hyperfine Spin of a Cs Atom Ensemble
We demonstrate quantum control of a large spin-angular momentum associated
with the F=3 hyperfine ground state of 133Cs. A combination of time dependent
magnetic fields and a static tensor light shift is used to implement
near-optimal controls and map a fiducial state to a broad range of target
states, with yields in the range 0.8-0.9. Squeezed states are produced also by
an adiabatic scheme that is more robust against errors. Universal control
facilitates the encoding and manipulation of qubits and qudits in atomic ground
states, and may lead to improvement of some precision measurements.Comment: 4 pages, 4 figures (color
Generalized Pseudopotentials for Higher Partial Wave Scattering
We derive a generalized zero-range pseudopotential applicable to all partial
wave solutions to the Schroedinger equation based on a delta-shell potential in
the limit that the shell radius approaches zero. This properly models all
higher order multipole moments not accounted for with a monopolar delta
function at the origin, as used in the familiar Fermi pseudopotential for
s-wave scattering. By making the strength of the potential energy dependent, we
derive self-consistent solutions for the entire energy spectrum of the
realistic potential. We apply this to study two particles in an isotropic
harmonic trap, interacting through a central potential, and derive analytic
expressions for the energy eigenstates and eigenvalues.Comment: RevTeX 4 pages, 1 figure, final published versio
Reply to "Comment on "Some implications of the quantum nature of laser fields for quantum computations''''
In this revised reply to quant-ph/0211165, I address the question of the
validity of my results in greater detail, by comparing my predictions to those
of the Silberfarb-Deutsch model, and I deal at greater length with the beam
area paradox. As before, I conclude that my previous results are an
(order-of-magnitude) accurate estimate of the error probability introduced in
quantum logical operations by the quantum nature of the laser field. While this
error will typically (for a paraxial beam) be smaller than the total error due
to spontaneous emission, a unified treatment of both effects reveals that they
lead to formally similar constraints on the minimum number of photons per pulse
required to perform an operation with a given accuracy; these constraints agree
with those I have derived elsewhere.Comment: A reply to quant-ph/0211165. Added more calculations and discussion,
removed some flippanc
Minimal Informationally Complete Measurements for Pure States
We consider measurements, described by a positive-operator-valued measure
(POVM), whose outcome probabilities determine an arbitrary pure state of a
D-dimensional quantum system. We call such a measurement a pure-state
informationally complete (PSI-complete) POVM. We show that a measurement with
2D-1 outcomes cannot be PSI-complete, and then we construct a POVM with 2D
outcomes that suffices, thus showing that a minimal PSI-complete POVM has 2D
outcomes. We also consider PSI-complete POVMs that have only rank-one POVM
elements and construct an example with 3D-2 outcomes, which is a generalization
of the tetrahedral measurement for a qubit. The question of the minimal number
of elements in a rank-one PSI-complete POVM is left open.Comment: 2 figures, submitted for the Asher Peres festschrif
Chaos, entanglement and decoherence in the quantum kicked top
We analyze the interplay of chaos, entanglement and decoherence in a system
of qubits whose collective behaviour is that of a quantum kicked top. The
dynamical entanglement between a single qubit and the rest can be calculated
from the mean of the collective spin operators. This allows the possibility of
efficiently measuring entanglement dynamics in an experimental setting. We
consider a deeply quantum regime and show that signatures of chaos are present
in the dynamical entanglement for parameters accessible in an experiment that
we propose using cold atoms. The evolution of the entanglement depends on the
support of the initial state on regular versus chaotic Floquet eigenstates,
whose phase-space distributions are concentrated on the corresponding regular
or chaotic eigenstructures. We include the effect of decoherence via a
realistic model and show that the signatures of chaos in the entanglement
dynamics persist in the presence of decoherence. In addition, the classical
chaos affects the decoherence rate itself.Comment: 11 pages, 9 figure
Distribution and determinants of patient satisfaction in oncology with a focus on health related quality of life
<p>Abstract</p> <p>Background</p> <p>Cancer patients usually undergo extensive and debilitating treatments, which make quality of life (QoL) and patient satisfaction important health care assessment measures. However, very few studies have evaluated the relationship between QoL and patient satisfaction in oncology. We investigated the clinical, demographic and QoL factors associated with patient satisfaction in a large heterogeneous sample of cancer patients.</p> <p>Methods</p> <p>A cohort of 538 cancer patients treated at Cancer Treatment Centers of America<sup>® </sup>(CTCA) was assessed. A patient satisfaction questionnaire developed in-house by CTCA was used. It covered the following dimensions of patient satisfaction: hospital operations and services, physicians and staff, and patient endorsements for themselves and others. QoL was assessed using the European Organization for the Research and Treatment of Cancer Quality of Life Questionnaire (QLQ-C30). The clinical, demographic and QoL factors were evaluated for predictive significance using univariate and multivariate logistic regression.</p> <p>Results</p> <p>The mean age of our patient population was 54.1 years (SD = 10.5, range 17-86), with a slight preponderance of females (57.2%). Breast cancer (n = 124) and lung cancer (n = 101) were the most frequent cancer types. 481 (89.4%) patients were "very satisfied" with their overall experience. Age and several QoL function and symptom scales were predictive of overall patient satisfaction upon univariate analysis. In the multivariate modeling, only those with a score above the median on the fatigue measure (i.e. worse fatigue) had reduced odds of 0.28 of being very satisfied (p = 0.03).</p> <p>Conclusion</p> <p>Patient fatigue, as reported by the QoL fatigue scale, was an independent significant predictor of overall patient satisfaction. This finding argues for special attention and programs for cancer patients who report higher levels of fatigue given that fatigue is the most frequently reported symptom in cancer patients.</p
Spirituality and end-of-life care in disadvantaged men dying of prostate cancer
Despite the positive influence of spiritual coping on the acceptance of a cancer diagnosis, higher spirituality is associated with receipt of more high intensity care at the end of life. The purpose of our study was to assess the association between spirituality and type of end-of-life care received by disadvantaged men with prostate cancer.
We studied low-income, uninsured men in IMPACT, a state-funded public assistance program, who had died since its inception in 2001. Of the 60 men who died, we included the 35 who completed a spirituality questionnaire at program enrollment. We abstracted sociodemographic and clinical information as well as treatment within IMPACT, including zolendroic acid, chemotherapy, hospice use, and palliative radiation therapy. We measured spirituality with the Functional Assessment of Chronic Illness Therapy—Spiritual Well-Being questionnaire (FACIT-Sp) and compared end-of-life care received between subjects with low and high FACIT-Sp scores using chi-squared analyses.
A higher proportion of men with high (33%) versus low (13%) spirituality scores enrolled in hospice, although our analysis was not adequately powered to demonstrate statistical significance. Likewise, we saw a trend toward increased receipt of palliative radiation among those with higher spirituality (37% vs. 25%, PÂ =Â 0.69). The differences in end-of-life care received among those with low and high spirituality varied little by the FACIT-Sp peace and faith subscales.
End-of-life care was similar between men with lower and higher spirituality. Men with higher spirituality trended toward greater hospice use, suggesting that they redirected the focus of their care from curative to palliative goals
Impact of medical specialists' locus of control on communication skills in oncological interviews
SCOPUS: ar.jinfo:eu-repo/semantics/publishe
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